Channeled penetration of high power CO 2 laser beam into water

Results of experimental research and qualitative modeling of the process of channeled penetration of high-power (0.3 - 3.5 kW) CW-CO 2 laser beam into water are presented. Experiments were made on: laser power threshold for channel formation; channel development phase (10 -3 -10 -1 s); quasi-stationary phase. The experiments revealed that the depth and mean diameter of the channel fluctuate at fiequencies in the range of 1-10 2 s -1 . The channel depth is 3-6 cm at laser power of up to 3 kW, depending upon the conditions for heat exchange in the water vessel. The conclusion is made, based on a qualitative hydrodynamic model, that geometrical and dynamical parameters of the channel (its depth, mean diameter, the velocity of the depth increasing) depend upon the intensity of turbulent heat transfer from the channel liquid walls into the bulk of the liquid. Simultaneously, the noticeable role play the evaporative losses of laser energy inside the free space of the channel, filled with evaporating microdroplets, torn-off from liquid walls of the channel by the process of capillary-evaporative instability. The principal point of the physical model consists in the assumption that energy and momentum balances of the channel can be attributed to radial transfer of vapor condensation enthalpy into liquid walls and to the equilibrium of dynamic pressure of vapor radial flow impinging the walls with the sum of hydrostatic and Laplacian pressures of the liquid.